This invention relates to a safety unit. In particular it is concerned with a safety unit for use in building structures.
In the course of building a structure such as a warehouse or office building which is to have a ridged roof then once the main building structure is in place there arises the need to erect on the upper part of the structure a spaced sequence of pre-fabricated trusses for the eventual roof. These are located between the walls and then secured. However raising a truss into position and securing it accurately in place is a hazardous operation for the building operatives involved. The open structure beneath the roofing level provides little or no support or protection for such operatives when working in the vicinity of the trusses.
As a safety feature it is commonly proposed that a net be located in the structure beneath the roofing level. However a stretched out net while serving to prevent an operative falling any significant distance from the lower part of the truss down through the structure tends to restrict the freedom of operation of the operatives. In addition the provision of further structural members to the operatives (such as long roofing members to be incorporated into the roof structure between the trusses) involves dismantling the net or nets to a greater or lesser extent. As a result it is not unknown for operatives to save time by avoid using a net or nets which omission is not necessarily in their own best interests from the point of view of their safety.
According to a first aspect of the present invention there is provided a safety unit in the form of a network or mesh for location across an opening to receive and restrain an object falling into the opening characterised in that the network or mesh is in the form of a trellis comprising: a first array of parallel rigid members; a second array of parallel rigid members; and pivoting means whereby each member of the first array is pivotably attached to the majority of members of the second array so that the first and second arrays can be pivoted relative to one another between
a first, housed, configuration wherein the difference between the width of the trellis and the length of the trellis tends to a maximum; and
a second, opened, configuration wherein the difference between the width of the trellis and the length of the trellis tends to a minimum;
the trellis being adapted for horizontal location in at least its opened configuration in a zone into or through which falling objects tend to pass by being supported at or near the periphery of the trellis so as to retain falling objects contacting the trellis in a region lying within the periphery.
According to a first preferred version of the first aspect of the present invention the pivoting means provide for the first and second arrays to lie in a substantially common plane at least when in the housed or in the opened configurations.
According to a second preferred version of the first aspect of the present invention or of the first preferred version thereof the screen member when in the opened configuration supported at intervals around its periphery so as to provide a tensioned area of the screen member into which a falling object can fall to enable the motion of the falling object to be damped.
According to a second aspect of the present invention there is provided a method of providing for the retention of falling objects at an elevated location, such as on a building site, comprising a network or mesh for spreading across an opening through which an object could fall characterised by the steps of:
locating at the location a safety screen in the form of a trellis comprising a first and a second array of parallel rigid members;
linking the first array to the second array so that the majority of members of the first array are pivotably attached to the majority of members of the second array for movement relative to one another between a first, house, configuration wherein the difference between the width of the trellis and the length tends to a maximum; and a second, opened, configuration wherein the difference between the width of the trellis and its length is a minimum; and
supporting the trellis at or near its periphery so as to retain falling objects contacting the trellis in a region lying within the periphery.